This invention relates generally to a method and apparatus for processing an audio signal, and more particularly, to processing stereo audio signals so that the resulting sounds produce a higher degree of channel separation than is expected for a given speaker-listener environment.
Past attempts to enhance the spatial quality of conventional stereo recordings involve deriving a composite left and right signal. These signals are processed in such a way that a listener who hears the right processed signal with his left ear will perceive a spatial quality predicted by the processing. Listening to the processed signals with earphones produce the results. Results obtained with loudspeakers will vary according to the listener-speaker relationship as defined by the laws governing the propagation of acoustic energy in a closed environment.
Such past attempts have also sacrificed the integrity of the center channel, where the left and right speaker signals are -intended to be in phase. Such past attempts also do not allow the listener to adjust the processing algorithm for the particular arrangement of speakers employed.
What is needed is a technique to enhance the spatial quality of stereo recordings without incurring the drawbacks of the prior art described above.
A method of processing left and right audio signals is disclosed which reproduces the illusion of a center channel while achieving a perception by the listener of a wider speaker separation. This method is partly obtained by altering the spectral response of the left and right speaker signals to obtain left and right sets of odd and even Fourier Transforms having certain characteristics. These processed signals are re-combined with the unaltered left and right signals to produce an expanded separation image that appears to extend beyond the physical location of the actual left and right loudspeakers, and to simultaneously centralize center channel signals to a point located between the loudspeakers. The process is defined to accommodate a large range of differential propagation angles to conform to the requirements of a broad range of listening environments.